A. Holographic Stereograms
Holographic stereograms originated in the late 1960's, one of the earliest publications in the field being that of Dominic J. DeBitetto entitled "Holographic Panoramic Stereograms Synthesized from White Light Recordings," Applied Optics, Vol. 8, No. 8, August 1969, pages 1740-1741.
As explained in the DeBitetto article, in accordance with the most basic embodiment of this technique, a series of two-dimensional photographs of an object are taken at different perspectives and then sequentially projected onto a diffusion screen using a coherent light source. Each image on the screen is holographically recorded on a portion of a photographic plate using a reference beam and a vertical slit aperture located just in front of the plate. The slit aperture is moved between exposures so that the finished plate is composed of a series of strip holograms, each strip containing interference information regarding one of the two-dimensional images and the location of the slit aperture when that two-dimensional image was recorded.
Illumination of the finished plate with laser light reconstructs all of the two-dimensional images. It also reconstructs the location of the slit for each of the images. When a viewer's eyes are placed in the vicinity of the reconstructed slits, each eye sees a different perspective view. The viewer's mind fuses these views together and interprets them as a three dimensional object, thus achieving three dimensionality from two two-dimensional images, as in a conventional stereogram.
General discussions of holographic stereograms and more advanced embodiments of this technique, including embodiments in which the reconstruction can be performed using incoherent light, can be found in G. Saxby, Practical Holography, Prentice Hall, New York, 1988, pages 55-59 and 246-259; F. Unterseher, J. Hansen, and B. Schlesinger, Holography Handbook--Making Holograms the Easy Way, Ross Books, Berkeley, Calif., 1987, pages 288-293; King et al., "A New Approach to Computer-Generated Holography," Applied Optics, Vol. 9, 1970, pages 471-475; U.S. Pat. No. 3,832,027; W. Molteni, Jr., "Black and White Holographic Stereograms," Proceedings of the International Symposium on Display Holography, Vol. 1, 1982, pages 15-21; S. Benton, "Photographic Holography," SPIE, Vol. 391 Optics in Entertainment, 1983, pages 2-9; W. Molteni, Jr., "Natural Color Holographic Stereograms By Superimposing Three Rainbow Holograms," SPIE, Vol. 462 Optics in Entertainment II, 1984, pages 14-18; W. Molteni, Jr., "Computer-Aided Drawing of Holographic Stereograms," Proceedings of the International Symposium of Display Holography, Vol. 2, 1985, pages 223-230; and S. Benton, "Display Holography--An SPIE Critical Review of Technology," SPIE, Vol. 532 Holography, 1985, pages 8-13.
With regard to certain of the embodiments of the present invention, Iovine, U.S. Pat. No. 4,964,684, discloses the use of a liquid crystal display matrix to form the vertical slit aperture employed in preparing the strip holograms of a holographic stereogram; Benton, U.S. Pat. No. 4,445,749, discloses a process for producing a holographic stereogram which is substantially achromatic; and W. Molteni, Jr., "Shear Lens Photography for Holographic Stereograms," SPIE, Vol. 1461 Practical Holography V, 1991, pages 132-139, discloses the use of shear lens photography to prepare the two-dimensional images from which a holographic stereogram is constructed. Each of these techniques can be used in connection with the practice of the present invention.
The use of predistorted two-dimensional images to form an alcove holographic stereogram is discussed in Benton, U.S. Pat. No. 4,834,476. In one embodiment, a series of undistorted perspective views are decomposed into columns and the columns are redistributed among the views to provide the desired predistortion. In another embodiment, anamorphic ray tracing is used to achieve the predistortion. Significantly, with regard to the present invention, predistortions suitable for use with an alcove stereogram are not suitable for use with a heads-up or heads-down display of the type disclosed herein.